Getting "Error: Using $this when not in object context" when saving attached image field

[Enkrod]

System
Joomla! 3.6.5 Stable [ Noether ] 1-December-2016 22:46 GMT
PHP Version 7.0.14-nmm1

Version
fieldsattach_j3 3.5.1.6 through 3.5.1.8

Description
Whenever I try to save an Article or Category with an attached Image Field, no matter if the field is filled or not, I get the following error:

An error has occurred.
0 Using $this when not in object context

Trials
Happenes ONLY with image field. As long as none is present, everything's dandy.
Upload-Type or height don't matter.

Notes
Saving seems to work, error only an annoyance right now.

[Enkrod]

See #67. Thanks to @iwan127

[Hertak]

I have same issue but with file field. I want update but is impossible this field is used on almost all