Fields with '=' as value stored in summary index are not extracted

[darshan]

I am storing a certain dataset in summary index which has some events with fields where the values are '=' or '=='. When searched, these events does not such fields. 

I managed to replicate this by doing this,

| makeresults 
| eval testval1 = "=" 
| eval testval2 = "==" 
| eval testval3 = "-" 
| eval testval4 = "--" 
| eval testval5 = "*" 
| eval testval6 = "/" 
| table testval* 
| summaryindex index="a_summary_index" name="testval"

which returns,

testval1	testval2	testval3	testval4	testval5	testval6	testval7	testval8
=	==	-	--	*	/	+	++

index="a_summary_index" source="testval" 
| table testval*

 returns,

testval1	testval2	testval3	testval4	testval5	testval6	testval7	testval8
		-	--	*	/	+	++

(where the testval1 and testval2 are null). The raw event looks like this,

testval1="=", testval2="==", testval3="-", testval4="--", testval5="*", testval6="/", testval7="+", testval8="++"

The sourcetype is by default (as all other configurations) is stash.

Field extractions configuration is,

[stash_extract]
DELIMS = ",", "="
CAN_OPTIMIZE = false
MV_ADD = true
CLEAN_KEYS = false

I was wondering if there will be any implications on other search features if the above stanza is modified (since this is default configuration). Any feedbacks or suggestions are much appreciated.