There is a often said sayings:
वैयाकरणकिरातादपशब्दमृगाः क्व यान्ति सन्त्रस्ताः। ज्योतिर्नट-विट-गायक-भिषगानन-गह्वराणि यदि न स्युः ॥
The first among them is astrologers, who quote often Sanskrit verses wrongly to impress their customers and nothing to mention in writing. नट and विट-s are the next and there were at a time, गायक-s who learnt under versatile scholars, who could pronounce correctly, but generally they too want to impress their audience without any heed for the pronunciation of the Sanskrit words, dragging them to fit their talent of singing. The above discussed is such one, by the popular singers and there is no use in correcting their pronunciation and if they pronounce correctly, their audience used to the songs, will complain and blame they are wrongly singing.
Purushottama deva in his Shabdabheda Sangraha, has collected the usages of shift of short and long vowels in many words he has seen:
फेणा फेणिस्तथाब्ध्यादौ करिण्यां कारिणीति च । धरित्री धारयित्री च तरीषी तारीषी तथा ॥४५॥
etc. Many of halanta-s are used as रजस्, रजस etc. श्वन्, श्वान, etc. श्वानं युवानं मघोनमेकपदे etc. verse.
As linguists say, phonetic changes are bound to take place during a span of duration in the development of any language. Apart from these, the above verse shows the ways of popularity even with अपशब्दाः।