Part-of-speech problems about adjectives or adverbs preceding 地 In "高兴/地/说", is 高兴 an adjective or an adverb?

The following link is a document on "Part-Of-Speech Tagging Guidelines for the
Penn Chinese Treebank (3.0)"

https://repository.upenn.edu/cgi/viewcontent.cgi?article=1039&amp;context=ircs_reports

The Chinese Treebank 8.0 data can be downloaded from 
https://wakespace.lib.wfu.edu/bitstream/handle/10339/39379/LDC2013T21.tgz?sequence=1

I am building a Chinese part-of-speech tagger model using the Ontonotes corpus, which contains Penn Chinese Treebank data. After reviewing many of the annotated sentences, I fail to understand the annotation of many 'VA' adjectives that precede (的/地(DEV) verb(VV)). I processed the annotated sentences into a file, and by regular expression I found that words in this case are twice more likely to be annotated as VA than to be annotated as AD.

In my impression, regarding "XXX 地 verb", XXX is always an adverb. But in the corpus, hundreds of cases like this are annotated as an adjective, like "可以/VV/O 轻易/VA/O 地/DEV/O 改变/VV/O", ..., etc. 

See page 14 of the document. 高兴 seems to be an adverb (AD) instead of an adjective (VA). 



Why are the words like this annotated as VA instead of AD? How to tell whether words of this case should be annotated as VA, JJ, or AD ? Or are the part-of-speech tags of the words really correctly annotated in the Chinese Treebank data?
Adjective is placed before noun and Adverb is placed before verb
So in your Context &quot;高兴/地/说&quot;, since 说 is a verb, 高兴地 will be an adverb.
高兴 itself can be a noun, adjective or adverb depending on the context and any preposition character following it.
的 is used before nouns , e.g. 灿烂的笑容 charming smile, it served as a possessive particle too
地 is used before verbs , e.g. 用力地踢 kick it hardly, 仔细地观察 observe carefully
得 is used before adjectives, the words before 得 are usually verbs. e.g. 扫得很干净 Sweep very clean, 做得很好 nicely done
more examples:
通过仔细的观察，我们可以知道一个人的喜好 By observing carefully, we can know a person's preferences  (观察 is a noun here)
他仔细地观察，不错过任何蛛丝马迹 He observes carefully and does not miss any clues (观察 is a verb here)
需要观察得很仔细，才能够分辨出两者有何不同 Need to observe carefully to be able to tell the difference between the two
Note: in contemporary and unofficial writing nowadays, you may find out more people to use 的 instead of 地 or 得 in those specific situations. e.g. 做的好！/ 悄悄的离开了 / 悄悄的来到我身边 which are however grammatically inaccurate but somehow accepted by the public. If you google it, tons of people are actually using it with lots of examples that you can find it online and therefore it has become a norm nowadays.
more reference for 的/地/得 usage here