Strange bug where <string>.replace(...) does not work.

In one of my scripted assertion I need to replace a substring with another value. For some strange reason that doesn't work:

My expression reads:

${=context.endpoint.replace("http","https")}

... but for some odd reason the resulting link still starts with "http://" instead of "https://" ?!?

To debug this I tried the following:

endpoint: ${=context.endpoint}
result1: ${=context.endpoint.replace("http","https")}
result2: ${=context.endpoint.replace('http','https')}

but the result still reads:

endpoint: http://chbbatscsoa01:9895/references_v2.0.0

result1: http://chbbatscsoa01:9895/references_v2.0.0

result2: http://chbbatscsoa01:9895/references_v2.0.0

According to the docs, both arguments of the replace()-method are simple strings (i.e. no reg. exps. or such), so why does this simple replace(...) not work? What am I missing here???