diff --git a/share/demo/release/capmpr.mod b/share/demo/release/capmpr.mod
new file mode 100644
index 0000000000..40abd43d13
--- /dev/null
+++ b/share/demo/release/capmpr.mod
@@ -0,0 +1,90 @@
+:  capump.mod plus a "reservoir" used to initialize cai to desired concentrations
+
+UNITS {
+	(mM) = (milli/liter)
+	(mA) = (milliamp)
+	(um) = (micron)
+	(mol) = (1)
+	PI = (pi) (1)
+	FARADAY = (faraday) (coulomb)
+}
+
+NEURON {
+	SUFFIX capmpr
+	USEION ca READ cao, cai WRITE cai, ica
+	GLOBAL k1, k2, k3, k4
+	GLOBAL car, tau
+}
+
+STATE {
+	pump	(mol/cm2)
+	pumpca	(mol/cm2)
+	cai	(mM)
+}
+
+PARAMETER {
+	car = 5e-5 (mM) : ca in reservoir, used to initialize cai to desired concentrations
+	tau = 1e9 (ms) : rate of equilibration between cai and car
+
+	k1 = 5e8	(/mM-s)
+	k2 = .25e6	(/s)
+	k3 = .5e3	(/s)
+	k4 = 5e0	(/mM-s)
+
+	pumpdens = 3e-14 (mol/cm2)
+}
+
+CONSTANT {
+	volo = 1 (liter)
+}
+
+ASSIGNED {
+	diam	(um)
+	cao	(mM)
+
+	ica (mA/cm2)
+	ipump (mA/cm2)
+	ipump_last (mA/cm2)
+	voli	(um3)
+	area1	(um2)
+	c1	(1+8 um5/ms)
+	c2	(1-10 um2/ms)
+	c3	(1-10 um2/ms)
+	c4	(1+8 um5/ms)
+}
+
+BREAKPOINT {
+	SOLVE pmp METHOD sparse
+	ipump_last = ipump
+	ica = ipump
+}
+
+KINETIC pmp {
+	COMPARTMENT voli {cai}
+	COMPARTMENT (1e10)*area1 {pump pumpca}
+	COMPARTMENT volo*(1e15) {cao car}
+
+	~ car <-> cai		(1(um3)/tau,1(um3)/tau)
+	~ cai + pump <-> pumpca		(c1,c2)
+	~ pumpca     <-> pump + cao	(c3,c4)
+
+	: note that forward flux here is the outward flux
+	ipump = (1e-4)*2*FARADAY*(f_flux - b_flux)/area1
+
+        : ipump_last vs ipump needed because of STEADYSTATE calculation
+        ~ cai << (-(ica - ipump_last)*area1/(2*FARADAY)*(1e4))
+
+	CONSERVE pump + pumpca = (1e10)*area1*pumpdens
+}
+
+INITIAL {
+	:cylindrical coordinates; actually vol and area1/unit length
+	voli = PI*(diam/2)^2 * 1(um)
+	area1 = 2*PI*(diam/2) * 1(um)
+	c1 = (1e7)*area1 * k1
+	c2 = (1e7)*area1 * k2
+	c3 = (1e7)*area1 * k3
+	c4 = (1e7)*area1 * k4
+
+	SOLVE pmp STEADYSTATE sparse
+}
diff --git a/test/hoctests/tests/test_many_ions.py b/test/hoctests/tests/test_many_ions.py
index c08eb55941..05bff06cb5 100644
--- a/test/hoctests/tests/test_many_ions.py
+++ b/test/hoctests/tests/test_many_ions.py
@@ -7,6 +7,7 @@
 from neuron import h, load_mechanisms
 from platform import machine
 import sys
+import io
 
 
 # return True if name exists in h
@@ -45,7 +46,50 @@ def exists(name):
 mt.select("ca_ion")
 assert mt.selected() > nion
 
+
+# return stderr output resulting from sec.insert(mechname)
+def mech_insert(sec, mechname):
+    # capture stderr
+    old_stderr = sys.stderr
+    sys.stderr = mystderr = io.StringIO()
+
+    sec.insert(mechname)
+
+    sys.stderr = old_stderr
+    return mystderr.getvalue()
+
+
 # test if can use the high mechanism index cadifpmp (with USEION ... WRITE cai) along with the high mechanims index ca_ion
 s = h.Section()
 s.insert("cadifpmp")
 h.finitialize(-65)
+# The ion_style tells whether cai or cao is being written
+istyle = int(h.ion_style("ca_ion", sec=s))
+assert istyle & 0o200  # writing cai
+assert (istyle & 0o400) == 0  # not writing ca0
+# unfortunately, at present, uninserting does not turn off that bit
+s.uninsert("cadifpmp")
+assert s.has_membrane("cadifpmp") is False
+assert int(h.ion_style("ca_ion", sec=s)) & 0o200
+# nevertheless, on reinsertion, there is no warning, so can't test the
+# warning without a second mechanism that WRITE cai
+assert mech_insert(s, "cadifpmp") == ""
+assert s.has_membrane("cadifpmp")
+# uninsert again and insert another mechanism that writes.
+s.uninsert("cadifpmp")
+assert mech_insert(s, "capmpr") == ""  # no warning
+assert mech_insert(s, "cadifpmp") != ""  # now there is a warning.
+
+# more serious test
+# several sections with alternating cadifpmp and capmpr
+del s
+secs = [h.Section() for i in range(5)]
+for i, s in enumerate(secs):
+    if i % 2:
+        assert mech_insert(s, "capmpr") == ""
+    else:
+        assert mech_insert(s, "cadifpmp") == ""
+
+# warnings due to multiple mechanisms at same location that WRITE cai
+assert mech_insert(secs[2], "capmpr") != ""
+assert mech_insert(secs[3], "cadifpmp") != ""