regex doesn't work: my error or bug?

[zandar]

Hi Gintaras,
this regex (PCRE flavour) finds the substring between two single quotes:

Code:

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(?<=')(.*?)(?=')

It works well when tested in RegexBuddy 4, 

in https://regexr.com and https://www.regexpal.com:

 

but if fails in QM:

Code:

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str userNamePattern username risultato
username="WHERE nomepass = 'testname'"
userNamePattern = "(?<=')(.*?)(?=')"
if(findrx(username userNamePattern 0 0 risultato 2)>=0)
    out risultato
else
    mes "match for ''(?<=')(.*?)(?=')'' not found" "Error"

is it my fault?

Again thank you for your exceptional support.