My textbook just taught me about っぱなし and how it indicates that X wasn't followed by Y as it is usually expected. It also taught me that this expresses that this fact is perceived negatively by the speaker.
What it didn't explicitely teach me is how it functions syntactically ^^ So far, I noticed that it is only used in this way:
Subject + が + verbっぱなし
This pattern even extended into sentences like this one: 1週間前から階段の前にバイクが置きっぱなしにしてある。
where the verb in use 置く confuses me a bit since I only encountered it in the pattern
subject + を + 置く
In addition, whatever rules the things coming AFTER っぱなし follow is still kind of a mystery for me. I frequently see っぱなし being followed by the copula as in my first example.
However sometimes it is also followed by something like in example 2. I would guess now that っぱなし is a noun? In this case, from a grammatical point of view, both the copula and the example 2 case would be viable I guess? If it should be the case that っぱなし is a noun I would expect a fixed set of particles being required for constructions like in example2 since the
complex feels like in the function of an attribute or adverb here, and therefore I'd usually expect something like の or に.