WB_FormulaSwitchToShorthand: Replace only full stimset names

We must not just replace stimset names as two stimsets might have the same
ending substring.

By just replacing only full words we avoid the issue without having to
change what we store in WPT.

Bug introduced in the initial version in 9b80987 (WaveBuilder: Add new
epoch type Combine, 2015-11-12).

Packages/MIES/MIES_WaveBuilder.ipf

@@ -2158,7 +2158,7 @@ End
 Function/S WB_FormulaSwitchToShorthand(variable channelType, string formula)
 
 	variable numSets, i
-	string stimset, shorthand
+	string stimset, shorthand, regex
 
 	if(isEmpty(formula))
 		return ""
@@ -2171,7 +2171,8 @@ Function/S WB_FormulaSwitchToShorthand(variable channelType, string formula)
 		shorthand = epochCombineList[i][%Shorthand]
 		stimset   = epochCombineList[i][%stimset]
 
-		formula = ReplaceString(stimset + "?", formula, shorthand)
+		regex = "(?i)\\b\\Q" + stimset + "\\E\\b\?"
+		formula = ReplaceRegexInString(regex, formula, shorthand)
 	endfor
 
 	return formula

Packages/tests/Basic/UTF_WaveBuilder.ipf

@@ -357,3 +357,23 @@ Function WB_StimsetWithNoEpochsAreNotSaved()
 
 	CHECK_EQUAL_STR(ST_GetStimsetList(searchString = basename + "*"), "")
 End
+
+Function CombineStimsetSubStrings()
+
+	string setNameA, setNameAA, setNameCombine
+
+	setNameA  = ST_CreateStimSet("setABC", CHANNEL_TYPE_DAC)
+	setNameAA = ST_CreateStimSet("newsetABC", CHANNEL_TYPE_DAC)
+
+	setNameCombine = ST_CreateStimSet("setCombine", CHANNEL_TYPE_DAC)
+
+	ST_SetStimsetParameter(setNameCombine, "Total number of epochs", var = 1)
+	ST_SetStimsetParameter(setNameCombine, "Type of Epoch 0", var = EPOCH_TYPE_COMBINE)
+
+	ST_SetStimsetParameter(setNameCombine, "Combine epoch formula version", epochIndex = 0, str = WAVEBUILDER_COMBINE_FORMULA_VER)
+	ST_SetStimsetParameter(setNameCombine, "Combine epoch formula", epochIndex = 0, str = LowerStr(setNameA) + "?" + " + " + LowerStr(setNameAA) + "?")
+
+	WAVE/Z wv = WB_CreateAndGetStimSet(setNameCombine)
+	CHECK_WAVE(wv, NUMERIC_WAVE)
+	CHECK_NO_RTE()
+End